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\(\frac{2}{4}+\frac{2}{28}+\frac{2}{70}+\frac{2}{130}+\frac{2}{208}\)
= \(\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}\)
= \(\frac{2}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{13.16}\right)\)
= \(\frac{2}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\right)\)
= \(\frac{2}{3}.\left(1-\frac{1}{16}\right)\)
= \(\frac{2}{3}.\frac{15}{16}\)
= \(\frac{5}{8}\)
2/4 + 2/28 + 2/70 + 2/130 + 2/208
= 2/1.4 + 2/4.7 + 1/7.10 + 1/10.13 + 1/13.16
= 2/3.(1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + 1/13 - 1/16)
= 2/3.(1 - 1/16)
= 2/3.15/16
= 5/8
P/s: "." là nhân nhé :V
a,
36 x 40 = (36 x 4) x 10 = 144 x 10 = 1 440
72 x 60 = (72 x 6) x 10 = 432 x 10 = 4 320
89 x 50 = (89 x 5) x 10 = 445 x 10 = 4 450
b,
450 x 70 = (45 x 7) x 100 = 315 x 100 = 31 500
2300 x 500 = (23 x 5) x 10 000 = 115 x 10 000 = 1 150 000
17 000 x 30 = (17 x 3) x 10 000 = 510 000
1. Rút gọn phân số:
\(\dfrac{100}{75}=\dfrac{100:25}{75:25}=\dfrac{4}{3}\)
\(\dfrac{28}{14}=\dfrac{28:14}{14:14}=\dfrac{2}{1}=2\)
\(\dfrac{70}{21}=\dfrac{70:7}{21:7}=\dfrac{10}{3}\)
2. Cộng phân số:
\(\dfrac{4}{5}+\dfrac{5}{5}=\dfrac{4+5}{5}=\dfrac{9}{5}\)
\(\dfrac{6}{9}+\dfrac{2}{9}=\dfrac{6+2}{9}=\dfrac{8}{9}\)
\(\dfrac{3}{8}+\dfrac{5}{8}=\dfrac{3+5}{8}=\dfrac{8}{8}=1\)
1.
\(\dfrac{100}{75}=\dfrac{4}{3};\dfrac{28}{14}=2;\dfrac{70}{21}=\dfrac{10}{3}\)
2.
\(\dfrac{4}{5}+\dfrac{5}{5}=\dfrac{4+5}{5}=\dfrac{9}{5}\\ \\ \\ \dfrac{6}{9}+\dfrac{2}{9}=\dfrac{6+2}{9}=\dfrac{8}{9}\\ \\ \\ \dfrac{3}{8}+\dfrac{5}{8}=\dfrac{3+5}{8}=\dfrac{8}{8}=1\)
Câu 1
A=21/4
B=3/16
C=41/8
D=1/2
Câu 2
Phải trồng tất cả:
280:70=4(cây)
Tick đi
a )3/4+3/4:(2/3:2-1/6)
=3/2 : 1/3-1/6
=3/2 : 1/6
=9
b) 3/4-3/4:(2/3:2x4)
= 0 :1/3 x4
= 0 : 4/3
= 0
c ) 7-8/4+3/4:6
=5 +1/8
=41/8
d)4:5/4-3+3/10
=16/5 -33/10
= - 1/10
2 giải phải trồng cột là:
280:70=4( cột )
ĐS : 4 cột
tick nha
Ta có:
\(\frac{3}{4}+\frac{3}{28}+\frac{3}{70}+\frac{3}{130}+\frac{3}{208}\)
\(=\frac{3}{1\times4}+\frac{3}{4\times7}+\frac{3}{7\times10}+\frac{3}{10\times13}+\frac{3}{13\times16}\)
\(=\frac{4-1}{1\times4}+\frac{7-4}{4\times7}+\frac{10-7}{7\times10}+\frac{13-10}{10\times13}+\frac{16-13}{13\times16}\) \(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\)
\(=1-\frac{1}{16}\)
\(=\frac{15}{16}\)
Chắc chắn đúng nhé !
\(\frac{2}{3}x\frac{1}{6}x\frac{9}{11}=\frac{1}{11}\)
\(2x3x\frac{4}{2}x3x4=144\)
học tốt
\(\frac{1}{2}+x\times\frac{3}{4}=2\)
\(x\times\frac{3}{4}=2-\frac{1}{2}\)
\(x\times\frac{3}{4}=\frac{3}{2}\)
\(x=\frac{3}{2}:\frac{3}{4}\)
\(x=\frac{3}{2}\times\frac{4}{3}\)
\(x=2\)
1/2 + x * 3/4 = 2
x * 3/4 = 2 - 1/2
x * 3/4 = 3/2
x = 3/2 : 3/4
x = 3/2 * 4/3
x = 2
Ta có: \(\frac{2}{5}.\frac{7}{4}-\frac{2}{5}.\frac{3}{7}\)
\(=\frac{2}{5}.\left(\frac{7}{4}-\frac{3}{7}\right)\)
\(=\frac{2}{5}.\frac{37}{28}\)
\(=\frac{37}{70}\)